Not long ago rumors about Excite Truck supporting custom soudtracks through SD cards, but Nintendo did all they could to keep this information from the public. But now that IGN has recieved their final build of the Wii and it's software, there's nothing keeping them from releasing as much or as little information as they like.
Today they revealed that Excite Truck would officially support MP3 playback from SD cards, with a maximum of 100 tracks per card. No other Wii titles have been announced to support MP3s from SD cards, but lets hope that developers take notice. (*cough*EA*cough*. Madden & Need for Speed)
Thanks Wii_Rulez & Tonuchi
Excite Truck Custom Soudtrack Confirmed - IGN
I feel so happy that im being thanked.
Thats really awesome. I really like how the Xbox had a similar thing. Can't wait to listen to my zelda while playing excite truck... that will be weird.
Can't wait to listen to my zelda while playing excite truck
lol 
Gonna be awesome listening to Billy Talent, Sum 41, Green Day, and the like during games. 
It will be awesome to listen to your favorite songs while blasting through the levels.
this is great!. i already knoe what songs i using.